MaTrace: tracing the fate of materials over time and across products in open-loop recycling

Operational Framework to Quantify "Quality of Recycling" across Different Material Types

Many pledges and laws are setting recycling targets without clearly defining quality of recycling. Striving to close this gap, this study presents an operational framework to quantify quality of recycling. The framework comprises three dimensions: the Virgin Displacement Potential (VDP); In-Use Stocks Lifetime (IUSL); and Environmental Impact (EI). The VDP indicates to what extent a secondary material can be used as a substitute for virgin material; the IUSL indicates how much of a certain material is still functional in society over a given time frame, and the EI is a measure of the environmental impact of a recycling process. The three dimensions are aggregated by plotting them in a distance-to-target graph. Two example calculations are included on poly(ethylene terephthalate) (PET) and glass. The results indicate that the recycling of bottle and container glass collected via a deposit-refund system has the lowest distance-to-target, at 1.05, and, thus, the highest quality of recycling. For PET bottles, the highest quality of recycling is achieved in closed-loop mechanical recycling of bottles (distance to optimal quality of 0.96). Furthermore, sensitivity analysis indicates that certain parameters, e.g., the collection rate for PET bottles, can reduce the distance-to-target to 0.75 when all bottles are collected for recycling.

Quality of recycling: Urgent and undefined

Quality of recycling is a concept used by many authors in the scientific literature and the EU legislator. However, a clear definition of what is intended for quality of recycling and a framework for operationalising it is lacking. Most studies, while proposing indicators reflecting quality, leave the concept of quality largely undefined. Such lack of clarity is an obstacle to the conception of robust policies addressing recycling and circular economy. In this article, we review the available studies investigating on recycling quality, synthetize the approaches available and conclude suggesting a way forward for research to operationalise the definition to support circular economy policy measures and monitoring. Essentially, quality is not an on/off criterion. The definition of quality of recycling should consider that quality depends on technical characteristics of the recyclate, which determine if it is adequate (thus functional) for a certain end application or not. Furthermore, it should consider that the recyclate can be used in different end applications over different markets and that can be adequate for substitution of primary resources in certain applications, but less or not in others. At system-wide level, this results in a certain degree of virgin resource substitution. To this end, preserving functionality, i.e. minimising the recyclate loss of functions via functional recycling, is key. Drawing upon studies on waste management, life cycle assessment and resource dissipation, we link the concept of functionality to substitutability of virgin resources and broader suitability in the circular economy, striving to show the linkages between different perspectives.

Does it pay to develop a ground source heat pump system? Evidence from China

The application potential and environmental benefits of ground source heat pump (GSHP) systems have become the focal points of decarbonization in the building sector. Synchronized and scientific analysis of GSHP systems' environmental and economic performance, however, remains lacking. This study analyzes the application prospects of GSHP systems via a life cycle assessment-based life cycle costing method, and considers China's actual status quo. The internal and external annual costs of a GSHP system per square meter are $ 4.05 and $ 1.37, respectively. Electricity generation and steel production are key processes to improve the environmental performance of a GSHP system further. Compared with coal-based heating, a GSHP system can mitigate 65%-95% of the environmental impact and 85% of external costs, except for the metal depletion impact which is 1.5 times higher than that of coal-based heating. In Shandong Province, promoting GSHP systems can substitute up to 69.4% of the district heating area, which implies reductions in fossil depletion, greenhouse gas emissions, human health impact, ecosystem quality impact, and external costs by up to 2.37 × 10¹⁰ kg oil eq, 1.08 × 10¹¹ kg CO₂ eq, 3.87 × 10⁵ DALY, 1.18 × 10³ Species. year, and $ 2.51 × 10¹⁰, respectively. In consideration of environmental and economic aspects, a GSHP system can exhibit benefits compared with coal-based heating after 2.34 years of operation. To improve the economic and environmental performance of GSHP systems, a series of recommendations on financial subsidies, renewable energy development, inter-regional power transmission, steel scrap utilization, and hydrogen reduction steelmaking is provided.

Regional waste footprint and waste treatments analysis

This paper provides a detailed analysis of the waste footprint and waste treatments at subnational level, for Brussels, Flanders, and Wallonia. The paper details the waste footprint components into direct waste from households (disposed in bins), indirect waste generated upstream in the supply chains and induced by household consumption and waste materials from the degradation of in-use stocks. For each component, we analysed the contribution of waste types, products consumed and location where the waste was generated, as well as the associated treatments. The results show that Flanders had the highest total waste footprint in absolute terms; Brussels the highest direct waste in capita terms and Wallonia the highest indirect waste and stock depletion in capita terms. In each region, almost 78 ± 2% of the regional waste footprints were attributed to the consumption of food products, manufactured products and restaurants and accommodation services. For each region, around 45 ± 4% of the indirect waste was generated within its boundaries, 16 ± 9% in other regions and 39 ± 5% out of Belgium. Incineration was the predominant waste treatment type of the regional waste footprint, followed by recycling. Landfill was the second widely applied treatment for indirect waste. Results constitute key information relevant to enhance the waste data monitoring practices at regional level with effects at national level. We unveiled the waste footprint and associated treatments inherent to the interregional and international linkages. Results are also useful resources to substantiate waste management and circular economy policies, enacting on waste prevention and reduction, ecodesign and product lifetime extension.

Cobalt in end-of-life products in the EU, where does it end up? - The MaTrace approach

The use of cobalt has experienced a strong growth in the last decades. Due to its high economic importance and high supply risk, it has been classified as a critical raw material for the EU and other economies. Part of the EU's strategy is intended to secure its availability, through fostering its efficient use and recycling. The latter is affected by factors such as the amount of available end-of-life products, and their collection-to-recycling rate. A novel methodology to analyze the impact of these factors on the cobalt flows in society is the model MaTrace, which can track the fate of materials over time and across products. The MaTrace model was expanded, adapted, and applied to predict the fate of cobalt embedded in finished products in use in the EU, considering the underlying life cycle phases within the technosphere. Eleven scenarios were built, assessing different options in the implementation of relevant EU's policies. The flows were projected for a period of 25 years, starting in 2015. The results of the baseline scenario show that after 25 years, around 8% of the initial stock of cobalt stays in use, 3% is being hoarded by users, 28% has been exported, and 61% has been lost. The main contributors to the losses of the system are the non-selective collection of end-of-life products, and the export of end-of-life products, recycled cobalt and final products. The results of the scenarios show that higher collection-to-recycling rates and lower export could increase up to 50% the cobalt that stays in use.

Accounting for the dissipation of abiotic resources in LCA: Status, key challenges and potential way forward

The concept of resources or materials dissipation after their use in the technosphere has been increasingly considered in life-cycle based studies, applying Substance and Material Flow Analysis (SFA and MFA), Input-Output Analysis, and Life Cycle Assessment (LCA). However, there is currently no common understanding of what a dissipative flow is. This article first reviews 45 publications to describe the status of resource dissipation in life-cycle based studies, discussing how resource dissipation is usually defined, which temporal perspective is considered, which compartments of dissipation are distinguished, and which approaches (including the implementation of parameters) are considered to assess resource dissipation in a system. Moreover, this article proposes a comprehensive definition of resource dissipation, building from the literature review and focusing on abiotic resources. It then discusses this definition with respect to its potential implementation in LCA considering today's existing Life Cycle Inventory (LCI) datasets and best practices. Overall it shows that the LCA framework may be well suited to assess abiotic resource dissipation. In particular i) the compartments of dissipation usually considered in the literature are covered in LCA, and ii) LCI databases could be a source of information to be further used to quantify a set of flows defined as "dissipative", as commonly considered in SFA/MFA studies. However, major challenges are still faced before any potential routine implementation in LCA. The article accordingly discusses the potential way forward in the short-term (development and test of possible approaches), mid-term (towards satisfactory robustness, and consensus) and long-term (large-scale changes of LCI databases).

Data quality assessment framework for critical raw materials. The case of cobalt

Critical Raw Materials (CRMs) require a deep understanding of their societal metabolism, for which robust data and information are needed. However, despite the efforts to build reliable data, some CRMs such as cobalt, are still characterised by lack of data harmonization, lack of connection between datasets, and significant data unavailability. Together with data gaps filling, data quality is a crucial aspect to improve Material Flow Analysis (MFA) and Criticality Assessment (CA). Nevertheless, most of the methodologies for Data Quality Assessment (DQA) are not designed for these tools, but for others, e.g. life cycle assessment. The current research addresses the following challenges; a better understanding of the societal metabolism of CRMs; the development and implementation of DQA in MFA and CA; and a better understanding of the available data related to current cobalt flows in the EU technosphere. The underlying life cycle phases of CRMs within the technosphere were identified, together with 15 key parameters. A new DQA matrix was developed, which was subsequently applied to the full dataset collected for cobalt. The dataset was built considering seven high-end applications of cobalt. More than 300 values were gathered, which were analysed in function of different aspects, such as the country/region, and year. Through the data analysis and the application of the DQA framework, data gaps were identified due to low availability and/or low quality. It was concluded that the main deficiency of cobalt data is its reliability, due to lack of information regarding its generation method, and the incomplete stakeholder coverage.

Bridging Tools to Better Understand Environmental Performances and Raw Materials Supply of Traction Batteries in the Future EU Fleet

Sustainable and smart mobility and associated energy systems are key to decarbonise the EU and develop a clean, resource efficient, circular and carbon-neutral future. To achieve the 2030 and 2050 targets, technological and societal changes are needed. This transition will inevitably change the composition of the future EU fleet, with an increasing share of electric vehicles (xEVs). To assess the potential contribution of lithium-ion traction batteries (LIBs) in decreasing the environmental burdens of EU mobility, several aspects should be included. Even though environmental assessments of batteries along their life-cycle have been already conducted using life-cycle assessment, a single tool does not likely provide a complete overview of such a complex system. Complementary information is provided by material flow analysis and criticality assessment, with emphasis on supply risk. Bridging complementary aspects can better support decision-making, especially when different strategies are simultaneously tackled. The results point out that the future life-cycle GWP of traction LIBs will likely improve, mainly due to more environmental-friendly energy mix and improved recycling. Even though second-use will postpone available materials for recycling, both these end-of-life strategies allow keeping the values of materials in the circular economy, with recycling also contributing to mitigate the supply risk of Lithium and Nickel.

Integrating Circular Economy Strategies with Low-Carbon Scenarios: Lithium Use in Electric Vehicles

Electrification of the transport sector will support its decarbonization, yet significantly change material requirements. This calls for an integrated modeling approach internalizing metal demand-supply dynamics in low-carbon scenarios to support the Paris agreement on climate change and sustainable material circulation. Here we develop a step toward the integrated simulation of energy-materials scenarios by unifying a stock-flow dynamics model for low-carbon scenarios using linear programming. The modeling framework incorporates lithium supply from both mines and end-of-life (EoL) recycling for projected use in electric vehicles on a global basis. The results show that supply constraints, which could become apparent from around 2030 in the case of current recycling rates (<1%), would impede the deployment of battery electric vehicles (BEVs), leading to the generation of an additional 300 Mt-CO₂ of emissions for vehicle operation in 2050. Another important finding is that increasing the recycling rate to 80% could substantially relieve restrictions on the introduction of BEVs without requiring primary supply from natural deposits far beyond historical rates of expansion. While EoL recycling is important from a long-term perspective, an EoL-oriented strategy has little effect on the short/medium-term (such as to 2030) lithium demand-supply balance because of exponential demand growth and long living batteries. Importantly, findings in this study emphasize the necessity of tackling climate change and resource circulation in an integrated manner.

Global Circular Economy Scenario in a Multiregional Input-Output Framework

In a resource-constrained world of an estimated 10 billion people in 2050 with the same material aspirations of today's high-income nations, there is no question: The future economy will need to be circular. From a policy perspective, the question is whether averting catastrophic environmental impacts through an accelerated transition to a global circular economy can also deliver sustained growth and jobs. The adoption of circular economy measures will have a range of effects on both domestic and foreign supply chains. Multiregional input-output (MRIO) analysis models the interdependencies between industries and within and between countries as well as between intermediate and final goods producers and consumers. It provides a useful toolbox for assessing social, environmental, and economy-wide impacts of the adoption of the circular economy. We project the MRIO database EXIOBASE to 2030 on the basis of the exogenously given parameters of the International Energy Agency's Energy Technology Perspective (IEA ETP) 6-degree scenario. We compare this business-as-usual (BAU) scenario and an alternative circular economy scenario. The circular economy scenario considers more recycling, reducing (material efficiency increase), repair, and reuse in relation to the BAU scenario. The adoption of circular economy measures has diverse impacts on the economy and environmental pressures. Global material extraction is reduced by about 10% compared to the baseline, while the impact on employment is small but positive. In particular, the shift from resource extracting sectors to the service sector will provide more opportunities for high-skilled and female workers.

How will second-use of batteries affect stocks and flows in the EU? A model for traction Li-ion batteries

Although not yet developed in Europe, second-use of traction batteries enables an extension of their lifetime and potentially improves life cycle environmental performance. Li-ion batteries (LIBs) offer the most promising chemistry for traction batteries in electric vehicles (xEVs) and for second-use. Due to the novelty of the topic and the expected increase of e-mobility in the next decades, more efforts to understand the potential consequences of second-use of batteries from different perspectives are needed. This paper develops a dynamic, parameterised Material Flow Analysis (MFA) model to estimate stocks and flows of LIBs after their removal from xEVs along the specific processes of the european value-chain. Direct reuse, second-use and recycling are included in the model and parameters make it customisable and updatable. Focusing on full and plug-in electric vehicles, LIBs and energy storage capacity flows are estimated. Stocks and flows of two embedded materials relevant for Europe were also assessed (cobalt and lithium). Results showed that second-use corresponds to a better exploitation of LIBs' storage capacity. Meanwhile, Co and Li in-use stocks are locked in LIBs and their recovery is delayed by second-use; depending on the slower/faster development of second-use, the amount of Co available for recycling in 2030 ranges between 9% and 15% of Co demand and between 7 and 16% for Li. Uncertainty of inputs is addressed through sensitivity analysis. A variety of actors can use this MFA model to enhance knowledge of second-use of batteries in Europe and to support the effective management of LIBs along their value-chain.

Bibliometric and Systemic Analysis on Material Flow Mapping and Industrial Ecosystems

Global instability can be seen as a reflection of the increasing demand for natural resources and the reduction of personnel expenditures. Yet, this is often associated with industrial systems, whose main objectives are to increase productive capacity and reduce costs. This scenario identifies the need for changes in strategy establishment in the organization’s operation mode focusing on sustainable development. Industrial ecosystems, through the symbiotic relationship of industries, aim to achieve sustainability goals. Material flow mapping is essential for the construction of these industrial ecosystems. Hence, the present paper carries out a structured literature review process in order to identify the state of the art and the research opportunities on material flow mapping and industrial ecosystems. For the accomplishment of this research, the methodological procedure called Knowledge Development Process — Constructivist (ProKnow-C) was adopted. The bibliographic portfolio is represented by 35 articles of the research theme. Throughout the bibliometric analysis, a statistical analysis of the articles that compose the portfolio is presented. In the systemic analysis, the main research problems, the means of solving them and the detected opportunities about this research theme are identified. Finally, conclusions and recommendations for future research are presented.

Role of vehicle inspection policy in climate mitigation: The case of Japan

In 1951, the Japanese government introduced a vehicle safety inspection system and this system has an effect of shortening the 'economic' lifetimes of automobiles and increasing CO₂ emissions associated with vehicle life-cycle. This study develops an integrated assessment framework by combining dynamic discrete choice analysis with life-cycle environmental accounting analysis based on a dynamic stock model. From the empirical results, we found that (1) the economic lifetime of a Prius in the benchmark model is surprisingly short, 5.07 years, due to the strict car inspection system, and this replacement cycle has contributed to increasing CO₂ over time; and (2) abolishing car inspections at the third and fifth years would considerably contribute to reducing life-cycle CO₂ emissions associated with Prius sold during the study period, 1997 to 2016, accounting for approximately one million tons-CO₂ eq. over 20 years. Thus, we conclude that modifying the regulation policy with a focus on the car inspection system to induce car owners to keep their automobiles longer would have environmental benefits.

Configuration of Materially Retained Carbon in Our Society: A WIO-MFA-Based Approach for Japan

To achieve the goals of Paris Agreement, global society is directing much effort in substantially reducing greenhouse gas (GHG) emissions. In addition to energy-related efforts, prevention of carbon release into the atmosphere with carbon capture and storage (CCS) and/or utilization of biomass resources is considered indispensable to achieving the global objective. In this study, considering carbon-containing goods as carbon reservoirs in our society similar to forests and reservoirs enabling CCS, the flow of materially utilized carbon was quantified by input-output-based material flow analysis (IO-MFA). As a result, in 2011, 6.3 Mt-C of petroleum-derived carbon and 7.9 Mt-C of wood-derived carbon were introduced to the Japanese society as end-use products (e.g., automobiles and constructions) in various forms (e.g., plastics and synthetic rubbers). The total amount (14.2 Mt-C) corresponded to 4.1% (52.1 Mt-CO₂) of annual CO₂ emission in Japan in 2011. Subsequently, by referring to the technology that can treat carbon in the target forms in end-of-life products, the recoverability of carbon as a material has been discussed with respect to each form and end-use of carbon. By numerically showing the necessity and potential of implementing appropriate technologies, this study provides scientific direction for policymakers to establish a quality carbon cycle in our society.

An Extended Model for Tracking Accumulation Pathways of Materials Using Input–Output Tables: Application to Copper Flows in Japan

Recycling has become increasingly important as a means to mitigate not only waste issues but also problems related to primary resource use, such as a decrease in resource availability. In order to promote and plan future recycling efficiently, detailed information on the material stock in society is important. For a detailed analysis of material stocks, quantitative information on flows of a material, such as its accumulation pathways, final destinations, and its processing forms, are required. This paper develops a model for tracking accumulation pathways of materials using input–output tables (IOTs). The main characteristics of the proposed model are as follows: (1) accumulations in sectors other than the final demand sectors (i.e., endogenous sectors) are explicitly evaluated, (2) accumulations as accompaniments to products, such as containers and packaging, are distinguished from the products, and (3) processing forms of materials are considered. The developed model is applied to analyze copper flows in Japan using the Japanese IOTs for the year 2011. The results show that accumulations of copper in endogenous sectors were not negligibly small (9.24% of the overall flow). Although accumulations of copper as accompaniments were very small, they may be larger for other materials that are largely used as containers or packaging. It was found that the destinations of copper showed different characteristics depending on the processing forms.

Optimal Recycling of Steel Scrap and Alloying Elements: Input-Output based Linear Programming Method with Its Application to End-of-Life Vehicles in Japan

Importance of end-of-life vehicles (ELVs) as an urban mine is expected to grow, as more people in developing countries are experiencing increased standards of living, while the automobiles are increasingly made using high-quality materials to meet stricter environmental and safety requirements. While most materials in ELVs, particularly steel, have been recycled at high rates, quality issues have not been adequately addressed due to the complex use of automobile materials, leading to considerable losses of valuable alloying elements. This study highlights the maximal potential of quality-oriented recycling of ELV steel, by exploring the utilization methods of scrap, sorted by parts, to produce electric-arc-furnace-based crude alloy steel with minimal losses of alloying elements. Using linear programming on the case of Japanese economy in 2005, we found that adoption of parts-based scrap sorting could result in the recovery of around 94-98% of the alloying elements occurring in parts scrap (manganese, chromium, nickel, and molybdenum), which may replace 10% of the virgin sources in electric arc furnace-based crude alloy steel production.

Dynamic Model for the Stocks and Release Flows of Engineered Nanomaterials

Most existing life-cycle release models for engineered nanomaterials (ENM) are static, ignoring the dynamics of stock and flows of ENMs. Our model, nanoRelease, estimates the annual releases of ENMs from manufacturing, use, and disposal of a product explicitly taking stock and flow dynamics into account. Given the variabilities in key parameters (e.g., service life of products and annual release rate during use) nanoRelease is designed as a stochastic model. We apply nanoRelease to three ENMs (TiO₂, SiO₂ and FeO_x) used in paints and coatings through seven product applications, including construction and building, household and furniture, and automotive for the period from 2000 to 2020 using production volume and market projection information. We also consider model uncertainties using Monte Carlo simulation. Compared with 2016, the total annual releases of ENMs in 2020 will increase by 34-40%, and the stock will increase by 28-34%. The fraction of the end-of-life release among total release flows will increase from 11% in 2002 to 43% in 2020. As compared to static models, our dynamic model predicts about an order of magnitude lower values for the amount of ENM released from this sector in the near-term while stock continues to build up in the system.

Quantifying Recycling and Losses of Cr and Ni in Steel Throughout Multiple Life Cycles Using MaTrace-Alloy

Alloying metals are indispensable ingredients of high quality alloy steel such as austenitic stainless steel, the cyclical use of which is vital for sustainable resource management. Under the current practice of recycling, however, different metals are likely to be mixed in an uncontrolled manner, resulting in function losses and dissipation of metals with distinctive functions, and in the contamination of recycled steels. The latter could result in dilution loss, if metal scrap needed dilution with virgin iron to reduce the contamination below critical levels. Management of these losses resulting from mixing in repeated recycling of metals requires tracking of metals over multiple life cycles of products with compositional details. A new model (MaTrace-alloy) was developed that tracks the fate of metals embodied in each of products over multiple life cycles of products, involving accumulation, discard, and recycling, with compositional details at the level of both alloys and products. The model was implemented for the flow of Cr and Ni in the Japanese steel cycle involving 27 steel species and 115 final products. It was found that, under a high level of scrap sorting, greater than 70% of the initial functionality of Cr and Ni could be retained over a period of 100 years, whereas under a poor level of sorting, it could plunge to less than 30%, demonstrating the relevance of waste management technology in circular economy policies.

How Will Copper Contamination Constrain Future Global Steel Recycling?

Copper in steel causes metallurgical problems, but is pervasive in end-of-life scrap and cannot currently be removed commercially once in the melt. Contamination can be managed to an extent by globally trading scrap for use in tolerant applications and dilution with primary iron sources. However, the viability of long-term strategies can only be evaluated with a complete characterization of copper in the global steel system and this is presented in this paper. The copper concentration of flows along the 2008 steel supply chain is estimated from a survey of literature data and compared with estimates of the maximum concentration that can be tolerated in steel products. Estimates of final steel demand and scrap supply by sector are taken from a global stock-saturation model to determine when the amount of copper in the steel cycle will exceed that which can be tolerated. Best estimates show that quantities of copper arising from conventional scrap preparation can be managed in the global steel system until 2050 assuming perfectly coordinated trade and extensive dilution, but this strategy will become increasingly impractical. Technical and policy interventions along the supply chain are presented to close product loops before this global constraint.

Regional distribution and losses of end-of-life steel throughout multiple product life cycles-Insights from the global multiregional MaTrace model

Substantial amounts of post-consumer scrap are exported to other regions or lost during recovery and remelting, and both export and losses pose a constraint to desires for having regionally closed material cycles. To quantify the challenges and trade-offs associated with closed-loop metal recycling, we looked at the material cycles from the perspective of a single material unit and trace a unit of material through several product life cycles. Focusing on steel, we used current process parameters, loss rates, and trade patterns of the steel cycle to study how steel that was originally contained in high quality applications such as machinery or vehicles with stringent purity requirements gets subsequently distributed across different regions and product groups such as building and construction with less stringent purity requirements. We applied MaTrace Global, a supply-driven multiregional model of steel flows coupled to a dynamic stock model of steel use. We found that, depending on region and product group, up to 95% of the steel consumed today will leave the use phase of that region until 2100, and that up to 50% can get lost in obsolete stocks, landfills, or slag piles until 2100. The high losses resulting from business-as-usual scrap recovery and recycling can be reduced, both by diverting postconsumer scrap into long-lived applications such as buildings and by improving the recovery rates in the waste management and remelting industries. Because the lifetimes of high-quality (cold-rolled) steel applications are shorter and remelting occurs more often than for buildings and infrastructure, we found and quantified a tradeoff between low losses and high-quality applications in the steel cycle. Furthermore, we found that with current trade patterns, reduced overall losses will lead to higher fractions of secondary steel being exported to other regions. Current loss rates, product lifetimes, and trade patterns impede the closure of the steel cycle.

Global carbon benefits of material substitution in passenger cars until 2050 and the impact on the steel and aluminum industries

Light-weighting of passenger cars using high-strength steel or aluminum is a common emissions mitigation strategy. We provide a first estimate of the global impact of light-weighting by material substitution on GHG emissions from passenger cars and the steel and aluminum industries until 2050. We develop a dynamic stock model of the global car fleet and combine it with a dynamic MFA of the associated steel, aluminum, and energy supply industries. We propose four scenarios for substitution of conventional steel with high-strength steel and aluminum at different rates over the period 2010-2050. We show that light-weighting of passenger cars can become a "gigaton solution": Between 2010 and 2050, persistent light-weighting of passenger cars can, under optimal conditions, lead to cumulative GHG emissions savings of 9-18 gigatons CO2-eq compared to development business-as-usual. Annual savings can be up to 1 gigaton per year. After 2030, enhanced material recycling can lead to further reductions: closed-loop metal recycling in the automotive sector may reduce cumulative emissions by another 4-6 gigatons CO2-eq. The effectiveness of emissions mitigation by material substitution significantly depends on how the recycling system evolves. At present, policies focusing on tailpipe emissions and life cycle assessments of individual cars do not consider this important effect.